System and method for machine control

ABSTRACT

The disclosure describes a control system for controlling the movement of an implement associated with a machine. The control system includes a speed sensor, a grade control system, an implement position sensor, and a controller. The speed sensor is configured to generate a speed signal indicative of a machine speed. The grade control system is configured to generate a desired implement position signal indicative of a desired implement position. The implement position sensor is configured to generate an implement position signal indicative of a position of the implement. The controller is configured to generate a machine control command to move the implement as a function of the speed signal, the desired implement position signal, and the implement position signal.

TECHNICAL FIELD

The present disclosure relates generally to a control system, and moreparticularly to systems and methods for controlling an implement tomaximize machine productivity and protect/improve a final grade.

BACKGROUND

Earthmoving machines such as track type tractors, motor graders,scrapers, and/or backhoe loaders, have an implement such as a dozerblade or bucket, which is used on a worksite in order to alter ageography or terrain of a section of earth. The implement may becontrolled by an operator or by an autonomous grade control system toperform work on the worksite. For example, the operator may move anoperator input device that controls the movement of the implement usingone or more hydraulic actuators. To achieve a final surface contour or afinal grade, the implement may be adjusted to various positions by theoperator or the grade control system.

Positioning the implement, however, is a complex and time-consuming taskthat requires expert skill and diligence if the operator is controllingthe movement. Thus, it is often desirable to provide the autonomousgrade control system for the implement to simplify the operator control.Prior art systems that automatically control the implement are known.For example, U.S. Pat. No. 6,064,933 discloses an automatic controlsystem for positioning the implement of an earthmoving machine inaccordance with a stored sequence of control command signals.

SUMMARY

Disclosed is a control system for controlling the movement of animplement associated with a machine. The control system includes a speedsensor, a grade control system, an implement position sensor, and acontroller. The speed sensor is configured to generate a speed signalindicative of a machine speed. The grade control system is configured togenerate a desired implement position signal indicative of a desiredimplement position. The implement position sensor is configured togenerate an implement position signal indicative of a position of theimplement. The controller is configured to generate a machine controlcommand to move the implement as a function of the speed signal, thedesired implement position signal, and the implement position signal.

Further disclosed is a method for controlling the movement of animplement associated with a machine. The method includes sensing themachine speed, determining a desired implement position with a gradecontrol system, sensing a position of the implement, and generating amachine control command to move the implement as a function of themachine speed, the desired implement position, and the position of theimplement.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a machine having a control system in accordance withan exemplary embodiment of the present disclosure;

FIG. 2 illustrates the control system to control the movement of animplement in accordance with an exemplary embodiment of the presentdisclosure;

FIG. 3 illustrates a modulation map in accordance with an exemplaryembodiment of the present disclosure; and

FIG. 4 illustrates a process flow diagram for an exemplary method tocontrol a movement of an implement, according to an aspect of thepresent disclosure.

DETAILED DESCRIPTION

Reference will now be made in detail to specific embodiments orfeatures, examples of which are illustrated in the accompanyingdrawings. Generally, corresponding reference numbers will be usedthroughout the drawings to refer to the same or corresponding parts.

The present disclosure relates to systems and methods for controlling animplement to maximize machine productivity. An exemplary embodiment of amachine 100 is shown schematically in FIG. 1. The machine 100 may be amobile machine that performs operations associated with industries suchas mining, construction, farming, transportation, or the like. Forexample, the machine 100 may be a track type tractor or dozer, asdepicted in FIG. 1, a motor grader, or other earth-moving machine knownin the art. While the following detailed description describes anexemplary embodiment in connection with a track type tractor, it shouldbe appreciated that the description applies equally to the use of thepresent disclosure in other machines.

In an illustrated embodiment, the machine 100 includes a power source102 and an operator's station or cab 104. The machine 100 furtherincludes an implement 108, such as, for example, a blade or a shovel formoving earth. The cab 104 may include a user interface 110 necessary tooperate the machine 100. The user interface 110 may include, forexample, one or more operator input devices 106 for propelling themachine 100 and/or controlling other machine components. The one or moreoperator input devices 106 may include one or more joysticks providedwithin the cab 104, and adapted to receive input from an operatorindicative of a desired movement of the implement 108.

For simplification purposes, only one operator input device 106 embodiedas a joystick will be discussed and shown in the figures. The userinterface 110 may also include a display for conveying information tothe operator and may include a keyboard, touch screen, or any suitablemechanism for receiving input from the operator to control and/oroperate the machine 100, the implement 108, and/or the other machinecomponents.

The implement 108 may be adapted to engage, penetrate, or cut thesurface of a worksite 112 and may be further adapted to move the earthto accomplish a predetermined task. The worksite 112 may include, forexample, a mine site, a landfill, a quarry, a construction site, or anyother type of worksite. Moving the earth may be associated with alteringthe geography at the worksite 112 and may include, for example, agrading operation, a scraping operation, a leveling operation, amaterial removal operation, or any other type of geography alteringoperation at the worksite 112.

In the illustrated embodiment, the implement 108 includes a cutting edge114 that extends between a first end 116 and a second end 118. The firstend 116, of the cutting edge 114 of the implement 108, may represent aright tip or right edge of the implement 108 and the second end 118, ofthe cutting edge 114 of the implement 108, may represent a left tip orleft edge of the implement 108. In an embodiment, the implement 108 maybe moveable by one or more hydraulic mechanisms operatively connected tothe operator input device 106 provided in the cab 104.

The hydraulic mechanisms may include one or more hydraulic liftactuators 120 and one or more hydraulic tilt actuators 122, for movingthe implement 108 to various positions, such as, for example, liftingthe implement 108 up or lowering the implement 108 down, and tilting theimplement 108 left or right. In the illustrated embodiment, the machine100 includes one hydraulic lift actuator 120 and one hydraulic tiltactuator 122 on each side of the implement 108. The illustratedembodiment shows two hydraulic lift actuators 120, but only one of thetwo hydraulic tilt actuators 122 is shown (only one side shown).Moreover, the hydraulic mechanism may also include one or more hydraulicpush cylinders (not shown) for pitching the implement 108 in forward orbackward direction.

The power source 102 may be an engine that provides power to a groundengaging mechanism 124 adapted to support, steer, and propel the machine100. The power source 102 may embody an engine such as, for example, adiesel engine, a gasoline engine, a gaseous fuel-powered engine, or anyother type of combustion engine known in the art. It is contemplatedthat the power source 102 may alternatively embody a non-combustionsource of power (not shown) such as, for example, a fuel cell, a powerstorage device, or another suitable source of power. The power source102 may produce a mechanical or electrical power output that may beconverted to hydraulic power for providing power to the ground engagingmechanism 124, the implement 108, and to other machine components.

The machine 100 may further include a control system 126 operativelyconnected to the operator input device 106 and to the hydraulicactuators 120, 122 for controlling movement of the implement 108. Asillustrated in FIG. 2, the control system 126 includes a load sensor128, a speed sensor 130, and an implement position sensor 132. In anembodiment, the load sensor 128 may include one or more torque sensorsor pressure transducers or temperature sensors or the like, associatedwith the power source 102 of the machine 100 and configured to generatea load signal indicative of a loading condition of the implement 108.Alternatively, the load sensor 128 may include strain gauges or pressuretransducers coupled to the implement 108 and/or the hydraulic actuators120, 122 to measure and quantify an amount of dirt/material carried bythe implement 108. In some alternative embodiments, the load sensor 128may include a system which estimates the loading condition of theimplement 108 as functions of other measured parameters. Load sensors128 are known by ordinary persons skilled in the art. The speed sensor130 may be associated with the ground engaging mechanism 124, andconfigured to generate a speed signal indicative of a machine speed. Inan alternative embodiment, the speed sensor 130 may be a systemassociated with a GPS system. Further, the implement position sensor 132may be associated with the implement 108 and/or the hydraulic actuators120, 122 and configured to generate an implement position signalindicative of a position of the implement 108.

The control system 126 further includes a grade control system 134, anda controller 136. The controller 136 is adapted to receive inputs fromthe operator input device 106 and/or the grade control system 134 tocontrol the movement of the implement 108 based on the loading conditionof the implement 108, the machine speed, and the position of theimplement 108 individually or collectively in pre-determinedcombinations. The grade control system 134 and the controller 136 mayinclude one or more control modules (e.g. ECMs, ECUs, etc.). The one ormore control modules may include processing units, memory, sensorinterfaces, and/or control signal interfaces (for receiving andtransmitting signals). The processing units may represent one or morelogic and/or processing components used by the control system 126 toperform certain communications, control, and/or diagnostic functions.For example, the processing units may be adapted to execute routinginformation among devices within and/or external to the control system126.

According to an aspect of the present disclosure, the controller 136 maydirect the implement 108 to move to a desired implement position inresponse to a desired position signal received from the grade controlsystem 134. The desired position signal is indicative of anautomatically determined position of the implement 108 by the gradecontrol system 134. The desired position signal indicative of theautomatically determined position of the implement 108 may include adesired elevational signal, such as, for example, the height it isdesired to have the blade 108 above the worksite 112. The desiredposition signal may or may not include a desired tilt angle of theblade. In an embodiment of the present disclosure, the controller 136may process the desired position signal, the speed signal, the implementposition signal, and the load signal to output a machine control commandto actuate the implement 108. As will be apparent to a person skilled inthe art, the machine control command may command an electrical currentof a determined magnitude, to actuate hydraulic valves 140, and 142associated with the hydraulic actuators 120 and 122, respectively.

Moreover, the automatically determined desired position of the implement108 may be based on an input received from a site design 138. The sitedesign 138 may include data related to a construction surface of theworksite 112 based on an engineering design. The construction surfaceprovided in the site design 138 may represent a ground profileindicative of an irregular three-dimension (3D) surface or a flat plane.As illustrated in FIG. 2, the construction surface is a design plane 144that represents a desired cutting plane or a final grade for theworksite 112. The grade control system 134 may be adapted to determine arelative desired location or position of the implement 108 with respectto the design plane 144. Moreover, the grade control system 134 may beadapted to determine a relative location or position of the machine 100within the worksite 112. The relative location or position of themachine 100 and/or the implement 108 may be determined using one or moreposition sensors, GPS receivers, and/or laser systems, which arewell-known in the art. In the illustrated embodiment, the grade controlsystem 134 receives the input from the site design 138 indicative of thedesign plane 144 for the worksite 112 and the relative position of theimplement 108 with respect to the design plane 144 and outputs thedesired position signal as a function of these inputs.

According to an embodiment of the present disclosure, the controller 136may include a modulation map 146, and a closed loop implement positioncontrol 148. The controller 136 is configured to process signals,received from the load sensor 128, and the speed sensor 130. Themodulation map 146 may include a number of data tables 150 to store anddynamically update load factors and speed parameters associated with themachine 100, based on the signals received from the load sensor 128 andthe speed sensor 130, respectively. In an embodiment, the load factorsmay represent normalized or pre-assigned values corresponding to theloading condition of the implement 108 during the operation, such as, alow load, a moderate load, and a high load. Further, the speedparameters may represent normalized or pre-assigned values based on atleast one of the machine speed, track pitch, and engine rpm. In anotherembodiment of the present disclosure, the modulation map 146 mayinclude, but not limited to, a set of modulation functions based onknown mathematical equations to dynamically update the data tables 150with the load factors and the speed parameters.

Further, the closed loop implement position control 148 may beconfigured to calculate and minimize an error value, which is indicativeof a difference between the position of the implement 108 determined bythe implement position sensor 132 and the automatically determineddesired position of the implement 108 by the grade control system 134.The closed loop implement position control 148 may include an adder 152adapted to combine or process the desired position signal, and theimplement position signal to output an implement position error signal.The implement position error signal is indicative of the error valuebased on the implement position signal and the desired position signal.It will be apparent to a person having ordinary skill in the art that,the adder 152 may act as an electronic signal multiplier or anelectronic mixer that combines two or more electrical or electronicsignals to output a composite signal. The adder 152 may includetransistors and/or diodes arranged in a circuit to achieve the purpose.

According to an embodiment of the present disclosure, the closed loopimplement position control 148 may include aproportional-integral-derivative controller (PID controller) using a PIDcontroller algorithm well known in the art. The closed loop implementposition control 148 may include a proportional control 154, an integralcontrol 156, and a derivative control 158. It may be apparent to aperson having ordinary skill in the art that, the PID controlleralgorithm may include a proportional gain factor (P), an integral gainfactor (I), and a derivative gain factor (D) associated with theproportional control 154, the integral control 156, and the derivativecontrol 158 respectively. The PID controller may scale the error valueas a function of the machine speed and/or the loading condition of theimplement. In an embodiment illustrated, the proportional gain factor(P), the integral gain factor (I), and the derivative gain factor (D)may include a dynamic proportional gain (G_(P)), a dynamic integral gain(G_(I)), and a dynamic derivative gain (G_(D)) which may be determinedas a function of the load signal and the speed signal.

Further, PID controller algorithm may include calculating and generatingthe machine control command as a function of a pre-determinedcombination of the proportional gain factor (P), the integral gainfactor (I), the derivative gain factor (D), and the implement positionerror signal. The machine control command may attempt to minimize theerror value, the difference between the position of the implement 108and the automatically determined position of the implement 108, bycontrolling the current to actuate hydraulic valves 140, and 142associated with the hydraulic actuators 120 and 122, respectively. Thecontroller 136 may further include a look-up table 160 including, butnot limited to, a set of modulation functions or a pre-defined look-uptable for validating the machine control command and output electricsignals corresponding to the current to actuate hydraulic valves 140,and 142.

FIG. 3 illustrates an exemplary modulation map 146, according to anembodiment of the present disclosure. As illustrated, the modulation map146 may include a set of two-dimensional arrays 162, 164, and 166 tostore the dynamic proportional gain (G_(P)), the dynamic integral gain(G_(I)), and the dynamic derivative gain (G_(D)) corresponding tovarious values of the load factors and speed parameters stored in thedata tables 150. In an exemplary embodiment, the two-dimensional array162 may include values for the dynamic proportional gain (G_(P))corresponding to a pre-determined combinations of load factors and speedparameters. Similarly, the two-dimensional arrays 164, 166 may includevalues for the dynamic integral gain (G_(I)), and the dynamic derivativegain (G_(D)), respectively, corresponding to the pre-determinedcombinations of load factors and speed parameters.

According to another aspect of the present disclosure, the controller136 may also direct the implement 108 to move to an operator determinedposition in response to an operator input signal received from theoperator input device 106. The operator determined position isindicative of a position representing an operator's desired movement ofthe implement 108. The operator input signal may also include anelevational signal, such as, for example, a lower implement signal or araise implement signal. The operator inputs signal indicative of theoperators' desired movement of the implement 108 may also include a tiltsignal, such as, for example, tilt left and tilt right signals. In anembodiment of the present disclosure, the controller 136 may process theoperator input signal and the load factor received from the data table150 to output the machine control command to move the implement 108.

Further, the controller 136 is adapted receive the operator input signalgenerated by the operator input device 106 or the grade control signalgenerated by the grade control system 134, and generate the machinecontrol command to move the implement 108 to the operator determinedposition or pre-determined target position, respectively. Thus, themachine control command actuates the hydraulic actuators 140, 142 tomove the implement 108 to the corresponding target position. Moving theimplement 108 may include a cut to the corresponding target position ora lift to the corresponding target position.

INDUSTRIAL APPLICABILITY

The industrial applicability of the systems and methods for controllingthe implement 108 to maximize machine productivity described herein willbe readily appreciated from the foregoing discussion. Although, themachine 100 is shown as a track-type tractor, the machine 100 may be anytype of machine that performs at least one operation associated with forexample mining, construction, and other industrial applications.Moreover, the systems and methods described herein can be adapted to alarge variety of machines and tasks. For example, backhoe loaders, skidsteer loaders, wheel loaders, motor graders, and many other machines canbenefit from the systems and methods described.

Conventional machines may use either the operator input signal or thedesired position signal from the automatic grade control system tocontrol the movement of the implement 108. Varying loading conditions ofthe implement 108 and speeds of the machine 100 may change the naturalfrequencies of the machine 100 and/or implement 108. Conventionalcontrol systems associated with the implement 108 are designed withfixed proportional, integral and derivative gains and it may becomeunstable when the machine speed and/or the loading condition of theimplement 108 are in some ranges. In such cases, the final grade orgrading quality may be not close to a desired one as the implement 108or the machine 100 may experience unanticipated resonance at a givenmachine speed and/or the loading condition of the implement 108. In anaspect of the present disclosure, the control system 126 receives theinputs corresponding to the load factor/speed parameters and controlsthe movement of the implement 108 to achieve the final grade as afunction of varying machine speed and/or the loading conditions of theimplement 108.

In accordance with the various embodiments, the control system 126 isadapted to process the desired position signal generated by the gradecontrol system 134 or the operator input devices 106, the load signal,and the speed signal to generate the machine control command to move theimplement 108. FIG. 4 illustrates a process flow diagram for anexemplary method 400 to control a movement of the implement 108,according to an aspect of the present disclosure. The method 400 may beimplemented by the controller 136.

At step 402 of the method 400, the controller 136 is adapted todetermine the desired implement position. The desired implement positionmay be determined either by the operator input device 106 or by theautomatic grade control system 134. In one embodiment, depicted by step404, where the desired implement position is determined by the operatorinput device 106, for example when an operator may move a joystick toindicate a position he/she desired the implement 108 to move to. Inanother embodiment, depicted by step 406, where the desired implementposition is determined by the automatic grade control system 134, thegrade control system 134 generates the desired implement positionsignal. The method 400 proceeds from step 402 to step 408.

At step 408, the controller 136 senses an actual position of theimplement 108 as a function of the implement position signal generatedby the implement position sensor 132. In an embodiment of the presentdisclosure, the method 400 may also include receiving varioussignals/inputs corresponding to a dirt/material condition of worksite112.

At step 410 the controller 136 is configured to sense the machine speedas a function of a speed signal generated by the speed sensor 130. Asdescribed above, the speed parameters corresponding to the sensedmachine speed may be dynamically updated in the modulation map 146.

At step 412, the controller 136 senses the loading condition of theimplement 108 as a function of the load signal generated by the loadsensor 128. The load factors corresponding to the sensed loadingcondition of the implement 108 may also be dynamically updated in themodulation map 146.

The machine 100 and/or the implement 108 may include a natural resonanceat some frequencies. These natural frequencies may change depending onthe machine speed and the loading condition of the implement 108. If aclosed loop control system also operates at one of the machine 100 orimplement 108 natural frequencies, the closed loop control system maybecome unstable. Using dynamic gains, determined as a function ofmachine speed and the loading condition of the implement 108, mayprevent instability.

At step 414, the controller 136 determines the dynamic proportional gain(G_(P)) as a function of the machine speed and the loading condition ofthe implement 108. As previously described in relation to FIG. 3, thecontroller 136 may include an exemplary modulation map 146. Themodulation map 146 may include the set of two-dimensional arrays 162storing the dynamic proportional gain (G_(P)) corresponding to variousvalues of the machine speed and the loading condition of the implement108. In one embodiment, the controller 136 may determine the dynamicproportional gain (G_(P)) through looking up the dynamic proportionalgain (G_(P)) in the modulation map 146. The method 400 proceeds to step416.

At step 416, the controller 136 determines the dynamic integral gain(G_(I)) as a function of the machine speed and the loading condition ofthe implement 108. The modulation map 146 may include the set oftwo-dimensional arrays 164, storing the dynamic integral gain (G_(I))corresponding to various values of machine speed and the loadingcondition of the implement 108. In one embodiment, the controller 136may determine the dynamic integral gain (G_(I)) through looking up thedynamic integral gain (G_(I)) in the modulation map 146. The method 400proceeds to step 418.

At step 418, the controller 136 determines the dynamic derivative gain(G_(D)) as a function of the machine speed and the loading condition ofthe implement 108. The modulation map 146 may include the set oftwo-dimensional arrays 166 storing the dynamic derivative gain (G_(D))corresponding to various values of machine speed and the loadingcondition of the implement 108. In one embodiment, the controller 136may determine the dynamic derivative gain (G_(D)) through looking up thedynamic derivative gain (G_(D)) in the modulation map 146. The method400 proceeds to step 420.

At step 420, the controller 136 may generate the machine command signalto move the implement 108 to the desired position as a function of thedesired position, the actual position, the dynamic proportional gain(G_(P)), the dynamic integral gain (G_(I)), and the dynamic derivativegain (G_(D)).

Aspects of this disclosure may also be applied to other machines.Although the embodiments of this disclosure as described herein may beincorporated without departing from the scope of the following claims,it will be apparent to those skilled in the art that variousmodifications and variations can be made. Other embodiments will beapparent to those skilled in the art from consideration of thespecification and practice of the disclosure. It is intended that thespecification and examples be considered as exemplary only, with a truescope being indicated by the following claims and their equivalents.

We claim:
 1. A control system for controlling movement of an implementassociated with a machine, the control system comprising: a speed sensorconfigured to generate a speed signal indicative of a machine speed; agrade control system configured to generate a desired implement positionsignal indicative of a desired implement position; an implement positionsensor configured to generate an implement position signal indicative ofa position of the implement; and a controller configured to generate amachine control command to move the implement as a function of the speedsignal, the desired implement position signal, and the implementposition signal, wherein the controller includes a closed loop implementposition control, and wherein the closed loop implement position controlincludes a proportional control including a dynamic proportional gain,the dynamic proportional gain determined as a function of apre-determined speed parameter.
 2. The control system of claim 1 furtherincluding, a load sensor configured to generate a load signal indicativeof a loading condition of the implement; and wherein the machine controlcommand is determined as a function of the load signal.
 3. The controlsystem of claim 1, wherein the grade control system is furtherconfigured to: receive an input related to a design plane from a sitedesign; determine a relative position of the implement with respect tothe design plane; and output the desired implement position signal as afunction of the design plane and the relative position of the implementwith respect to the design plane.
 4. The control system of claim 1,wherein the dynamic proportional gain is determined as a function of aload signal indicative of a loading condition of the implement.
 5. Acontrol system for controlling movement of an implement associated witha machine, the control system comprising: a speed sensor configured togenerate a speed signal indicative of a machine speed; a grade controlsystem configured to generate a desired implement position signalindicative of a desired implement position; an implement position sensorconfigured to generate an implement position signal indicative of aposition of the implement; and a controller configured to generate amachine control command to move the implement as a function of the speedsignal, the desired implement position signal, and the implementposition signal, wherein the controller includes a closed loop implementposition control configured to calculate and minimize an error value,the error value indicative of the difference between the position of theimplement and the desired position of the implement, and wherein theclosed loop implement position control includes an integral controlincluding a dynamic integral gain, the dynamic integral gain determinedas a function of the speed signal.
 6. The control system of claim 5,wherein the dynamic integral gain is determined as a function of a loadsignal indicative of a loading condition of the implement.
 7. A controlsystem for controlling movement of an implement associated with amachine, the control system comprising: a speed sensor configured togenerate a speed signal indicative of a machine speed; a grade controlsystem configured to generate a desired implement position signalindicative of a desired implement position; an implement position sensorconfigured to generate an implement position signal indicative of aposition of the implement; and a controller configured to generate amachine control command to move the implement as a function of the speedsignal, the desired implement position signal, and the implementposition signal, wherein the controller includes a closed loop implementposition control configured to calculate and minimize an error value,the error value indicative of the difference between the position of theimplement and the desired position of the implement, and wherein theclosed loop implement position control includes a derivative controlincluding a dynamic derivative gain, the dynamic derivative gaindetermined as a function of the speed signal.
 8. The control system ofclaim 7, wherein the dynamic derivative gain is determined as a functionof a load signal indicative of a loading condition of the implement. 9.A method for controlling movement of an implement associated with amachine, the method comprising: sensing a machine speed; determining adesired implement position with a grade control system; sensing aposition of the implement; and generating a machine control command, bya controller, to move the implement as a function of the machine speed,the desired implement position, and the position of the implement,wherein the controller includes a closed loop implement positioncontrol, and wherein the closed loop implement position control includesa proportional control including a dynamic proportional gain, thedynamic proportional gain determined as a function of a pre-determinedspeed parameter.
 10. The method of claim 9, further including: sensing aloading condition of the implement; and generating the machine controlcommand as a function of the loading condition of the implement.
 11. Themethod of claim 9, further including: receiving an input related to adesign plane from a site design; determining a relative position of theimplement with respect to the design plane; and determining the desiredimplement position as a function of the design plane and the relativeposition of the implement with respect to the design plane.
 12. A methodfor controlling movement of an implement associated with a machine, themethod comprising: sensing a machine speed; determining a desiredimplement position with a grade control system; sensing a position ofthe implement; generating a machine control command to move theimplement as a function of the machine speed, the desired implementposition, and the position of the implement; calculating and minimizingan error value with a closed loop implement position control, the errorvalue indicative of the difference between the position of the implementand the desired implement position; determining a proportional gainfactor for a proportional scaling of the error value as a function ofthe machine speed; and generating the machine control command as afunction of the proportional gain factor.
 13. The method of claim 12,further including: sensing a loading condition of the implement; anddetermining the proportional gain factor as a function of the loadingcondition of the implement.
 14. A method for controlling movement of animplement associated with a machine, the method comprising: sensing amachine speed; determining a desired implement position with a gradecontrol system; sensing a position of the implement; generating amachine control command to move the implement as a function of themachine speed, the desired implement position, and the position of theimplement; calculating and minimizing an error value with a closed loopimplement position control, the error value indicative of the differencebetween the position of the implement and the desired implementposition; determining an integral gain factor for an integral scaling ofthe error value as a function of the machine speed; and generating themachine control command as a function of the integral gain factor. 15.The method of claim 14, further including: sensing a loading conditionof the implement; and determining the integral gain factor as a functionof the loading condition of the implement.
 16. A method for controllingmovement of an implement associated with a machine, the methodcomprising: sensing a machine speed; determining a desired implementposition with a grade control system; sensing a position of theimplement; generating a machine control command to move the implement asa function of the machine speed, the desired implement position, and theposition of the implement; calculating and minimizing an error valuewith a closed loop implement position control, the error valueindicative of the difference between the position of the implement andthe desired implement position; determining a derivative gain factor fora derivative scaling of the error value as a function of the machinespeed; and generating the machine control command as a function of thederivative gain factor.
 17. The method of claim 16, further including:sensing a loading condition of the implement; and determining thederivative gain factor as a function of the loading condition of theimplement.